In its 1974 Lau v. Nichols decision, the U.S. Supreme Court stated that public schools have an obligation to provide appropriate language services to students who are learning English. As a result, today when a student enters public school for the first time in the United States, be it in kindergarten or at a point during high school, his or her need for English language services is evaluated. (In most states, students' proficiency in non-English languages is never screened or evaluated—Minnesota is a notable exception).
Nationally, there are standard practices for identifying, monitoring, and exiting dual language learners (DLLs) or English language learners (ELLs) from English as a Second Language (ESL) services. While many preschool programs also screen for language proficiency, there is substantial variability in states' screening policies and programs' use of these instruments; the standard practices outlined are specific to kindergarten through 12th grade.